1. Field of the Invention
The present invention relates to a method and a system for determining a region of interest in an image.
It finds application particularly in the automotive industry with, for example, the detection of visibility distance in foggy weather.
2. Description of the Related Art
With the development of electronic technologies, sensors and means of processing, many improvements have been proposed to make driving vehicles more safe or comfortable. Some of these improvements rely on analyzing an image of the environment around the vehicle to adapt handling of the vehicle handling or to inform the driver. Such is the case, for example, with systems for determining a visibility distance. These systems in particular are directed to adjusting the lighting of the vehicle according to the visibility distance.
In the known way, these systems include acquisition of an image and determination of a region of interest in this image intended to be processed in real time. Determination of a region of interest aims to exclude from the image the elements which would disturb its processing. It also enables the area of the image which is the object of the processing to be limited and consequently the quantity of data to be processed to be reduced. Thus, it offers the possibility of reducing the time and resources required for processing.
In existing systems, a region of interest is determined by using a “region growing” method. According to this method, the luminance of each pixel is analyzed and compared with the luminance of the pixels which are adjacent to it. If the variation of luminance is less than a preset threshold, then the region of interest is extended to these adjacent pixels so as to define a homogeneous area, if not these pixels are excluded from the region of interest. This method is in particular described in the document “A segmentation system based on thresholding. Graphical Models and Image Processing” [Käohler, 1981].
This method of region growing requires the luminance of each pixel to be determined and compared with the pixels which are adjacent to it. This method thus involves a considerable processing effort. It is consequently either not very robust, and does not then allow non-relevant elements to be removed from the region of interest, or extravagant in terms of computing time and use of resources. In practice, it has proven to be not very suitable for motor vehicles since this type of application requires rapid and reliable determination of the region of interest, at the same time limiting the cost price.
What is needed, therefore, is an improved approach for precisely delivering a region of interest in an image.